Being a Knight puts you above the smallfolk and opens up prospects but you are still beneath the landed nobility. You can say they are sort of a Quasi-Nobility (If they are not descended from nobility itself). Following are some benefits a Knight enjoys:
Knights can marry younger daughters of landed houses and thus climb up a step on social ladder like Ser Bronn of Blackwater did by marrying Lolys Stokeworth. A commoner can never hope to marry an aristocrat girl but Knights are considered a valid match for at least younger daughters of impoverished or minor houses. Ser Eustace Osgrey, head of a minor and diminished house from the Reach said he would have married his daughter Alysanne to Ser Duncan the tall if she were alive.
Nevertheless, Commonborn Knights are no fit consort for Ladies of major houses as Lady Rohanne Webber decided not to marry Duncan despite having feelings for him. She later went on to be grandmother of Lord Tywin Lannister. Quoting Rohanne Webber from The Sworn Sword:
"You are quite mad," The smoke had filled her eyes with tears. "If you
were better born, I would have married you"
Later she said:
I had to marry you know... my father's will. Oh don't be such a fool.
Similarly Ser Bonifer Hasty and Princess (Later Queen) Rhaella Targaryen loved each other but Bonifer could never hope to marry the princess because of his low birth. According to Barristan Selmy:
Their love was ultimately a brief thing and could never have been
otherwise, as Bonifer was of far too low birth to be considered as a
suitor for a princess of the royal line
In more recent events, Amerei "Gatehouse" Frey married a hedge knight named Pate of the Blue Fork. The unseemly match was made because Amerei was daughter of 9th son of Lord Walder Frey and was notorious for her promiscuity.
Knights can escape judgement of a lord for any crime by demanding a trial by combat. It might not save you but at least you don't get to be sentenced by some posh aristocrat. Ser Duncan the Tall used this right to escape judgment of lordlings for hitting Prince Aerion Targaryen. As Prince Baelor Breakspear told Ser Duncan in The Hedge Knight:
"You have another choice though", Prince Baelor said quietly. "Whether it
is a better choice or worse, I can not say, But I remind you that any
Knight accused of a crime has a right to demand trial by combat."
Knights can win renown and money by jousting (And winning) against rich nobles. Non-Knights can some times be allowed to joust as well like in Tourney of KL but there are events in which it is only reserved for Knights such as Tourney at Ashford. Quoting Plummer the Steward from The Hedge Knight:
Plummer pursed his lips. "My Lord's tourney is a contest for Knights.
Are you a Knight?"
Knights can officially and legally lay foundation of a new house by taking a name and forming their coat of Arms. For example, Artys Arryn who founded House Arryn was originally a knight. Their coat of Arms can only be inherited by their true-born sons. Bastards can not inherit or display the arms. A true-born daughter or son can display the arms but he can not call himself a Knight unless he is anointed and Knighted by some Knight. Quoting Prince Baelor from The Hedge Knight:
"By law, only a true born son is entitled to inherit a Knight's arms.
You must needs find a new device Ser, A sigil of your own."
Also Jon said in AGOT:
"Girls get the arms but not the swords. Bastards get the swords but
not the arms. I did not make the rules, little sister."
Knights can legally create new Knights & take squires. e.g. Ser Lyonel Baratheon knighted squire Raymun Fossoway. Ser Arthur Dayne knighted the squire Jaime Lannister. Ser Arlan of Pennytree apparently knighted his squire Duncan the Tall. Quoting Ser Lyonel Baratheon from The Hedge Knight:
"The lad has the truth of it," said Ser Lyonel Baratheon. "Do it, Ser
Duncan. Any knight can make a knight".
Knights are usually held in high esteem by common people and orders such as the Nights Watch. Knights are usually preferred to command at Night's Watch for different tasks for example Ser Wynton Stout was chosen as Castellan of Castle Black when Bowen Marsh went West to fight at bridge of Skulls. Sole reason for this appointment was that Stout was a knight. From ASOS, Jon's POV:
“If Marsh is gone, who did he name as castellan?”
The armorer laughed. “Ser Wynton, gods preserve him. Last knight in
the castle and all. The thing is, Stout seems to have forgotten and no
one’s been rushing to remind him. I suppose I’m as much a commander as
we have now. The meanest of the cripples.”
Similarly Jaime recalls that on his return from Harrenhal after being officiated as a Knight of Kingsguard, the bar keep refused to take money from him and said that this was a story to tell his grandchildren. From ASOS, Jaime's POV:
The innkeep had refused his coin. "It's an honor to have a knight of
the Kingsguard under my roof, ser," the man had said. "It's a tale
I'll tell my grandchildren."
But it can be said that this sort of special treatment comes with being a Knight of the Kingsguard or a Knight of massive fame.
Knights can hope to ransom themselves if they are bested in battle. Common soldiers are not taken captives and are usually slaughtered. Knights however can yield to their enemies in hopes to be ransomed later. From Tyrion's POV in ACOK:
“I yield, ser,” a different knight called out, farther down the river.
“Yield. Ser knight, I yield to you. My pledge, here, here.” The man
lay in a puddle of black water, offering up a lobstered gauntlet in
token of submission.
Also from Arya's POV in ACOK:
Gendry frowned. “Knights and lordlings, they take each other captive
and pay ransoms, but they don’t care if the likes of you yield or
Knights have better prospects at finding service than a common man at arms because Knights are thought to be valuable fighters due to their rigorous training which usually starts at childhood. Service with landed nobles can give them a chance to perform tasks which can in turn reward them with landed titles of their own from their liege. They can even rise to companionship of Kings as Knights of Kingsguard.
Knights are usually held in high esteem by the faith of seven because of their vows to defend the faith and because of knighthood being rooted in Andal religion. With reformation of faith militant, Knights can seek service there as well. Quoting from a Feast For Crows, Brienne's POV:
When they saw the hedge knights, the begging brothers halted, and the
chanting died away. “Good knights,” one said, “the Mother loves you.”
Being a Knight has an impact on your love life as well. Westerosi Ladies seem to love the valiant Knights. Example would be the innkeep's daughter whose mother (The innkeep) complained about that to Ser Duncan the Tall:
"The girl turn to sighs and giggles everytime a knight rides by. I
swear I could not tell you why. Knights are built the same as other
Your word carries more weight if you swear it by "your honor as a knight". Same goes for your testimonies. Ferrymen on trident took Sandor Clegane on board when he swore a false oath on his honor as a knight to pay them when they were across. From ASOS, Arya's POV:
“How do I know you’re good for it?” the bent-backed man asked, after a
moment. He’s not, she wanted to shout. instead she bit her lip.
“Knight’s honor,” the Hound said, unsmiling. He’s not even a knight.
She did not say that either.
“That will do.” The ferryman spat.
Knights are thought to be a boost to prestige of a diplomatic mission especially if they are descended from some noble house. We saw this when Petyr Baelish demanded Knights should accompany him at his meeting with Tyrells. From AFFC, Tyrion POV, Baelish said:
“And forty more-twenty knights with as many squires. If I arrive
without a knightly tail, the Tyrells will think me of small account.”
Knights can support other Knights in trials of seven. e.g. Ser Lyonel Baratheon joined Ser Duncan the Tall in his trial against Prince Aerion. Quoting Prince Maekar from A Hedge Knight:
"Don’t play the fool, it will not serve. It must be seven against
seven. You must needs find six other knights to fight beside you."
Also Quoting Ser Steffon Fossoway from A Hedge Knight:
“Raymun the Reluctant,” mocked his cousin Ser Steffon. An apple made
of gold and garnets fastened his cloak of yellow wool. “You need not
fear, cousin, this is a knightly combat. As you are no knight, your
skin is not at risk. Ser Duncan, you have one Fossoway at least. The
ripe one. I saw what Aerion did to those puppeteers. I am for you.”
Knights can be offered a chance to join Night's Watch as Tywin Lannister offered Ser Alliser Thorne & Ser Jaremy Rykker a chance to Join NW or be beheaded. But this is not exclusive to Knights, commonfolk can also be offered that chance. From AGOT, Tyrion's POV:
Ser Jaremy Rykker commented dryly. “I ought to know, I was there on
the battlements beside him (Thorne). Tywin Lannister gave us a
splendid choice. Take the black, or see our heads on spikes before
evenfall. No offense intended, Tyrion.”
Knights can sit in viewing gallery with nobles in a tourney. Quoting Ser Raymun Fossoway from The Hedge Knight:
"Well met lad," Ser Raymun said easily. "Ser Duncan, why not watch
from the viewing gallery? All knights are welcome there."
Knights can demand a Trial of Seven and accept challenges of their opponents to it if they wish. Ser Damon Morrigen accepted challenge of King Maegor the Cruel's mother to prove Maegor's unworthiness to throne. A trial of seven took place
but it is not clear who asked for it, The crown or the Warrior's sons? It is most likely that Damon Morrigen and fellow Warrior's sons demanded that form, being zealots and everything, demanded by Ser Damon. However Maegor fought & won, emerging as sole survivor. Similarly Prince Aerion Targaryen demanded a trial of Seven when Ser Duncan the Tall demanded a trial of combat in The Hedge Knight.
"A trial of seven,” said Prince Aerion, smiling. “That is my right, I
“Or mayhap they simply had a taste for swordplay,” said Lord Leo
Tyrell, a cynical smile touching his lips. “Regardless, Ser Aerion is
within his rights. A trial of seven it must be.”
FREE FOOD AT WEDDINGS!!!! It is considered bad luck to refuse to host a knight on one's wedding among the nobles. So Knights are always welcome at noble weddings. Ser Duncan the Tall enjoyed this benefit at wedding of Lord Butterwell with daughter of Lord Frey. Quoting from The Mystery Knight, Ser Duncan notices:
Though uninvited, the three of them had been welcomed to the feast
quick enough; It was ill luck to refuse a knight hospitality on your
However Knighthood does not guarantee lands. A knight may or may not be landed.
A Song of Ice and Fire mostly lead us through life of nobility. If you want a closer view of life of a Knight, specially a Knight with no noble lineage, I would highly recommend reading the Dunk & Egg series which has been recently compiled into a single volume called "A Knight of the Seven Kingdoms".